Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

Dynamic positioning and way-point tracking of underactuated AUVs in the presence of ocean currents

Abstract: This paper addresses the problem of dynamic positioning and way-point tracking of underactuated autonomous underwater vehicles (AUVs) in the presence of constant unknown ocean currents and parametric model uncertainty. A nonlinear adaptive controller is proposed that steers an AUV so as to track a sequence of points consisting of desired positions (x, y) in an inertial reference frame, followed by vehicle positioning at the final target point. The controller is first derived at the kinematic level assuming that the ocean current disturbance is known. An exponential observer is then designed and convergence of the resulting closed loop system trajectories is analyzed. Finally, integrator backstepping and Lyapunov based techniques are used to extend the kinematic controller to the dynamic case and to deal with model parameter uncertainty. Simulation results are presented and discussed.

A xenogeneic-free bioreactor system for the clinical-scale expansion of human mesenchymal stem/stromal cells

Abstract: The large cell doses (>1 × 10(6) cells/kg) used in clinical trials with mesenchymal stem/stromal cells (MSC) will require an efficient production process. Moreover, monitoring and control of MSC ex-vivo expansion is critical to provide a safe and reliable cell product. Bioprocess engineering approaches, such as bioreactor technology, offer the adequate tools to develop and optimize a cost-effective culture system for the rapid expansion of human MSC for cellular therapy. Herein, a xenogeneic (xeno)-free microcarrier-based culture system was successfully established for bone marrow (BM) MSC and adipose tissue-derived stem/stromal cell (ASC) cultivation using a 1L-scale controlled stirred-tank bioreactor, allowing the production of (1.1 ± 0.1) × 10(8) and (4.5 ± 0.2) × 10(7) cells for BM MSC and ASC, respectively, after 7 days. Additionally, the effect of different percent air saturation values (%Airsat ) and feeding regime on the proliferation and metabolism of BM MSC was evaluated. No significant differences in cell growth and metabolic patterns were observed under 20% and 9%Airsat . Also, the three different feeding regimes studied-(i) 25% daily medium renewal, (ii) 25% medium renewal every 2 days, and (iii) fed-batch addition of concentrated nutrients and growth factors every 2 days-yielded similar cell numbers, and only slight metabolic differences were observed. Moreover, the immunophenotype (positive for CD73, CD90 and CD105 and negative for CD31, CD80 and HLA-DR) and multilineage differentiative potential of expanded cells were not affected upon bioreactor culture. These results demonstrated the feasibility of expanding human MSC from different sources in a clinically relevant expansion configuration in a controlled microcarrier-based stirred culture system under xeno-free conditions. The further optimization of this bioreactor culture system will represent a crucial step towards an efficient GMP-compliant clinical-scale MSC production system.